Articles formed from aligned fiber cured in a polyaspartic acid urethane matrix

ABSTRACT

A freestanding article is provided that uses a cured polyaspartic acid urethane resin to form a hardened matrix impregnating and surrounding a cloth having parallel fibers. This resin provides an article with superior mechanical and weathering properties relative to conventional resins such as epoxies and vinyl esters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 12/747,672filed on Jun. 11, 2010. Application PCT/US2008/086395 claims the benefitof U.S. Provisional Application 61/012,834 filed on Dec. 11, 2007 whichis incorporated herein by reference.

FIELD OF THE INVENTION

The present invention in general relates to articles formed from alignedfibers in a cured resin matrix and in particular to such articles havinga polyaspartic acid urethane matrix.

BACKGROUND OF THE INVENTION

The use of an aligned fiber sheet impregnated with curable resin is awell-established technique to form articles with high strength to weightratios. Stress skin articles formed through the use of an aligned fibersheet impregnated with curable resin illustratively include boat hulls,vehicle body panels, aircraft components, missile components,surfboards, prosthetics, and the like. Unfortunately, combinations ofaligned fibers with conventional monomers and resins cross linking toform thermoset polymers have failed to afford a package of completelydesirable properties. Prototypical of such aligned fiber sheet systemsis fiberglass impregnated with curable epoxy resins. Limitations in theuse of such articles are article performance and production techniques.

The incomplete ability of resin to wet a fiber leads to reduced pull outenergy from the fiber from a cured resin matrix resulting in lowerarticle strength. As curable resins are most often hydrophobic,silanization or other modification of glass fibers is accomplished torender the glass hydrophobic. While this is costly, it is effective toincrease article strength; however, many fiber materials are eitherdamaged or otherwise not amenable to surface modification to changefiber surface energies. High strength fibers such as carbon and aramidare representative of fibers that are comprised by certain surfacetreatments. Existing resins also suffer from erratic cure profiles,susceptibility of cure to ambient moisture and light, and articleyellowing after cure upon exposure to sunlight.

The toxicity, odor, and other negative handling attributes of resinshave also limited the application for aligned fiber containing curedmatrix articles. As an ever increasing number of resins are found tohave toxicity even in cured articles, the applications have accordinglydiminished for fiber containing cured matrix materials. Additionally,the increased requirements on curing environment, worker safety andventilation further limit the locations of usage. This has had aparticularly large impact on field repair of articles.

Thus, there exists a need for an oriented fiber reinforced thermosetmaterial having improved performance, handling, and weatherabilityrelative to conventional resins.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 is photographic images of an inventive cured polyaspartic acidurethane on a test strip (right) and a like thickness convention curedepoxy after six months of simulated aging.

SUMMARY OF THE INVENTION

A freestanding article is provided that uses a cured polyaspartic acidurethane resin to form a hardened matrix impregnating and surrounding acloth having parallel fibers. This resin provides an article withsuperior mechanical and weathering properties relative to conventionalresins such as epoxies and vinyl esters.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has utility as an oriented fiber reinforcedthermoset resin article. The present invention in resorting to apolyaspartic acid urethane thermoset precursor that is conventionallyused in forming protective floor coatings, oriented fiber reinforcedfreestanding articles are produced having superior flexural andweathering characteristics relative to conventional resins used to wetoriented fiber cloths. The use of this resin system as a cure matrix fororiented fiber cloths shows an attractive set of properties relative toconventional resins such as epoxies for the formation of freestandingarticles such as boat hulls, vehicle body panels, aircraft components,missile components, surfboards, and prosthetics. An inventivepolyaspartic acid urethane is appreciated to also be beneficial as a tiecoat between dissimilar polymers which otherwise have poor adhesion. Aninventive polyaspartic acid urethane is appreciated to also bebeneficial as a tie coat between dissimilar polymers which otherwisehave poor adhesion.

The production of polyaspartic acid urethane from a two-part mixture ofa polyisocyanate component and an isocyanate reactive polyaspartic esterand a polyketamine is detailed in U.S. Pat. No. 5,623,045 andspecifically at column 3, line 2-column 6, line 35. Upon mixing of thepolyisocyanate with an isocyanate reactive polyaspartic acid ester andpolyketamine part B, cross linking occurs to produce urethane linkages.According to the present invention, a polyisocyanate part A preferablyhas an NCO content of between 10 and 25 total polyisocyanate polymerweight percent and a molecular weight of between 1000 and 10,000.Polyisocyanates operative herein illustratively include aliphaticpolyisocyanates such as hexamethylene-1,6-diisocyanate,2,2,4-trimethylhexamethylene-1,6-diisocyanate; alicyclic polyisocyanatessuch as cyclohexane-1,4-diisocyanate,dicyclohexylmethane-4,4′-diisocyanate, aryl polyisocyanates such asp-phenylene diisocyanate, toluene-2,4-isocyanate, and diphenyl methane2,4′-diisocyanate. Additionally, an isocyanate operative herein includespolyphenylene polymethylene polyisocyanate derived from condensation ofaniline and formalin, liquidified diphenylmethane diisocyanatescontaining carbodiimide groups or uretonimine groups, modifiedpolyisocyanates containing at least one urethane group, allophanategroup, biuret group or uretodione group. Other isocyanates operativeherein are modified polyisocyanates containing urethane groups,allophanate groups or uretodione groups such that the polyisocyanatesare liquid at the ambient temperature such as 20° C. Hexamethylenediisocyanate based polyisocyanates are representative of polyisocyanatesoperative herein.

The part B reactive polyaspartic acid ester with the polyisocyanate hasthe formula:

where X represents an n-valent radical which is inert towards isocyanategroups and obtained by removing the primary amino groups from an organicpolyamine having a number average molecular weight (MO of 60 to 6000 andcontaining n (cyclo)aliphatically bound amino groups; R¹ and R²represent the same or different alkyl radicals having 1 to 18 carbonatoms; and n represents a whole number of at least 2. Preferably, n isan integer of between 2 and 1000. R¹ and R² are linear, branched orcyclic allyls. A cyclic allyl is appreciated to also include acombination of a cyclic portion with a linear or branched portion.Polyamine precursors operative in the present invention illustrativelyinclude diamines such as C₂-C₂₄ linear aliphatic diamines, C₂-C₂₄branched aliphatic diamines, and aryl diamines and polymer backboneshaving the amines extending therefrom; and triamines such as aliphaticalkylene oxide triamines. Specific amines operative herein includeiso-octyl amine; 1,12 dodecadiamine; diethyl toluene diamine; andpolyoxypropylenetriamine (PPD) having a molecular weight of from 200 to5,000, with 200 to 600 being preferred. Preferably, the presentinvention incorporates as an amine component a triamine. Polyamineprecursors operative herein have a molecular weight of between 120 and5,000 Daltons. Preferably, a triamine of the present invention has amolecular weight of 200 to 600. Most preferably, a triamine precursor ofthe present invention has a molecular weight of about 400 Daltons. It isappreciated that a polyamine precursor that is a mixture of diamine,multiple diamines, and triamines is also operative herein. In a mixedamine component, preferably, the diamine of the present invention has alower molecular weight of between 200 and 2,500 Daltons and the triaminehas a higher relative molecular weight of between 200 and 5,000 Daltons.It is appreciated that a triamine present in combination with a diaminewill provide branched polyureas that will form higher viscositythickening. When a triamine is present it is typically provided in astoichiometric ratio relative to a diamine of 0.01-25:1.

An additional optional component on the B side is a polyketamine of theformula:

wherein R³ and R⁴ may be the same or different and represent inertorganic radicals such as hydrocarbon radicals having up to 8 carbonatoms, preferably alkyl radicals having 1 to 8 carbon atoms, or theradicals R³ and R⁴, together with the carbon atom, may form a 5- or6-membered cycloaliphatic ring; R⁵ represents an (m+1)-valent radical,obtained by removing the primary amino groups from a polyamine having anumber average molecular weight (M_(n)) of 88 to 2000, having(cyclo)aliphatically bound amino groups and optionally containing oxygenand/or nitrogen atoms; and m is 1 to 3. Suitable polyamine precursors toa polyketamine of the present invention include those operative to form(I).

The relative ratio of polyaspartic acid ester (I) to polyketamine (II)typically ranges in a weight ratio of I:II of 90:10 to 10:90 andpreferably 80:20 to 20:80. More preferably, the moiety ratio ofisocyanate groups to isocyanate-reactive groups found in the B side isbetween 0.8:1 and 2:1 and preferably between 0.8:1 and 1.4:1.

It is appreciated that the cross-linkable resin according to the presentinvention optionally includes a solvent to facilitate spreading andwetting of a parallel fiber mat. Suitable solvents compatible with aninventive resin illustratively include ethyl acetate, butyl acetate,methoxypropyl acetate, methyl isobutyl ketone, xylene,N-methylpyrrolidone, petroleum ethers and combinations thereof.Preferably, a minimal or non-volatile organic content (VOC) resinformulation is used to facilitate indoor usage and limit respiratorycomplications associated with application or contact with a subsequentlycured product. It is appreciated that an inventive resin is amenable toinclusion with conventional resin additives illustratively includingpigments, fillers, plasticizers, catalysts, and antioxidants.

Upon combining A and B parts of an inventive resin, the resin is readilyapplied to a parallel fiber mesh by a known application technique suchas spraying, brushing, dipping and applying with the use of rollers ordoctor blades. Without intending to be limited to a particular theory,it appears that as-produced glass fiber and carbon fiber cloths bothhave stronger surface attraction to the resultant polyaspartic acidurethanes resulting in improved mechanical properties. This is furtherdetailed in the following exemplary examples. Preferably the inventiveresin is applied in an uncured state onto fiber cloths in an amount ofbetween 0.6 to 1.5 parts by weight resin per part by weight of alignedfiber cloth.

In order to evaluate the properties of an inventive polyaspartic acidcured urethane, a series of tests were performed relative to acorresponding epoxy cure technology known to provide high strengthcomposites with parallel fiber materials. Polyester and vinyl esterresins are not considered equivalent as they lack all of the desirablequalities of an epoxy. Properties of an inventive composite are furtherdetailed in the following nonlimiting examples.

Example 1 Inventive Resin

A polyisocyanate part A contains a homopolymer of hexamethylenediisocyanate (CAS No. 28182-81-2) having an NCO content of 18% and aviscosity of 700 megapascal·seconds at room temperature. Part B includesa polyaspartic ester according to Formula I formed from the condensationof 1 mole of 4,4′-diaminodicyclohexylmethane and 2 moles ofdiethylmalate having an equivalent weight of 280 grams per amine and aviscosity of 1500 megapasal·seconds at room temperature. Part B alsoincludes a ketamine formed from the condensation of1-amino-3,3,5-trimethyl-5-5-aminomethylcyclohexane and 2 moles of methylisobutyl ketone having an equivalent weight of 167 grams and a weightratio of polyaspartic ester to polyketamine of 3:1. The parts A and Bare mixed in an equivalent ratio of 1 between isocyanate groups of partA and groups reactive therewith from part B. Upon mixing of parts A andB, the uncured resin is applied to cloths as detailed below.

Comparative Epoxy Formulation Example

Resin Research Project's 21 System was used as a comparative and isbisphenol A based epoxy resin with a modified cycloaliphatic aminecuring agent. The epoxy resin was handled and cured per manufacturerspecifications. The resin is a bisphenol A resin based epoxy resin,modified cycloaliphatic amine curing agent system designed primarily formarine composite use. The physical state of the resin before cure ismedium viscosity water white to pale yellow liquid with a Color(Gardner) of 1 to 3. Physical properties of this resin after cure at 20°Celsius as measured two weeks after cure are provided in Table 1.

TABLE 1 Comparative Epoxy Physical Properties Resin/hardener 2000/2100Mix by Volume  2 to 1 Mix by Weight 100 to 45 Tensile Strength 9,800Tensile Modulus 405,000 Flexural Strength 14,800 Flexural Modulus480,000 Barcol Hardness 83 HDT 122 F. Compression Yield 15,400Elongation % 3.8

Example 2 Flex Out and Rate of Return

Ten strips that were 2.54 centimeters (cm) by 31.2 cm were laid up with1 layer of 170 gram S-fiberglass cloth sandwiched with 1 layer of 114gram S-fiberglass cloth, five each per Example 1 and Comparative EpoxyExample. The thickness was measured to be within 0.0025 cm for accuracyof the test. This is typical for the surfboard industry or other thinlaminations in other industries where weight, strength, and performanceare at a premium. The test was performed horizontally with a scale atone end to measure in grams. The 5 strips from each group were flexed to8.9 cm noting the amount of weight required to achieve this flexure.

Grams of weight to achieve 8.9 cm of flexure.Comparative epoxy: 95, 95, 85, 80, 75Inventive polyaspartic urethane: 105, 140, 105, 105, 125

Example 3 Flex Out Deformation

Strips of 2 layers of 170 gram S-fiberglass cloth and 4 layers of 114gram S-fiberglass cloth were laminated together, five each per Exhibit 1and Comparative Example. Test strips were 2.54 cm by 31.2 cm by 0.15thick. Test strips were flexed to 12.7 cm apart end to end then measuredon a flat surface for deformation. Then the strips were measured 30minutes later to see if they were still deformed.

Comparative epoxy: 0.64 cm, 0.95 cm, 0.79 cm, 0.56 cm, 0.95 cm, 6/16″Inventive polyaspartic urethane: 0, 0, 0.03 cm, 0.03 cm, 0.

Example 4 Torsional Twist Deformation

Ten strips per Example 3 were used, five each per Exhibit 1 andComparative Example. Strips were tested by twisting one end 120 degrees.The strips were measured in degrees of deformation.

Comparative epoxy: 18, 21, 10, 25, 16Inventive polyaspartic urethane: 1, 0, 3, 2, 1

Example 5 Flex Out to Cracking and Then to Failure

Ten test strips are the identical glass schedule of Example 3 withexception of length being 15.24 cm. The strips were put into a vise andmeasured until cracking occurred and then at lamination failure in whichone or more laminates within the strip broke in half.

Comparative epoxy cracking: 10.80 cm, 10.16 cm, 11.11 cm, 10.32 cm,10.48 cmInventive polyaspartic cracking: 6.35 cm, 6.67 cm, 6.35 cm, 6.67 cm,5.40 cmComparative epoxy failure: 8.57 cm, 7.62 cm, 8.26 cm, 8.26 cm, 7.95 cmInventive polyaspartic failure: 6.19 cm, 6.35 cm, 6.67 cm, 6.35 cm, 5.08cm

Example 6 Cosmetic Discoloration from UV Light and Weather

Samples of inventive resin and epoxy resin per Example 1 and ComparativeEpoxy

Example were cured to a like thickness on aluminum test strips and wereput into a weather cabinet for 24 hours. The cabinet stimulates weatheraging at a timeframe of 6 months.

FIG. 1 shows images of inventive polyaspartic urethane (right) and thecomparative epoxy (left) after simulated weathering. A discoloration ofthe epoxy test strip is noted while the inventive test strip cured resinis visually unchanged.

Example 7 Comparison to Vinyl Ester Resin

The tests of Example 2 are repeated with a cured vinyl ester resincomparative that is 66.5 weight percent vinyl ester resin in styrenewith a cobalt curative and commercially available as HYDREX 100-HF fromReichhold Inc. This comparative had a performance comparable to theExample 2 epoxy resin.

Patent documents and publications mentioned in the specification areindicative of the levels of those skilled in the art to which theinvention pertains. These documents and publications are incorporatedherein by reference to the same extent as if each individual document orpublication was specifically and individually incorporated herein byreference.

The foregoing description is illustrative of particular embodiments ofthe invention, but is not meant to be a limitation upon the practicethereof. The following claims, including all equivalents thereof, areintended to define the scope of the invention.

1. An article comprising: a parallel fiber cloth; and a curedpolyaspartic acid urethane resin impregnating said cloth.
 2. The articleof claim 1 wherein said cloth is fiberglass.
 3. The article of claim 1wherein said cloth is polyamide.
 4. The article of claim 1 wherein saidcloth is carbon fiber.
 5. The article of claim 1 wherein said cloth isformed as a surfboard.
 6. The article of claim 1 wherein said cloth isformed as a boat component.
 7. The article of claim 1 wherein said clothis formed as a prosthetic.
 8. The article of claim 1 wherein said clothis formed as a vehicle body component.
 9. The article of claim 1 furthercomprising a plurality of parallel fiber cloths, wherein each of saidplurality of cloths is independently fiberglass, polyamide, or carbonfiber.
 10. The article of any of claim 1 wherein said resin hashexamethylene subunits.
 11. The article of any of claim 1 wherein saidresin is present from 0.6 to 1.5 parts by weight per part of weight ofsaid cloth.
 12. The article of any of claim 1 wherein said resin has atleast one additive of a pigment, a filler, a flow aid, a plasticizer, acatalyst, or an antioxidant.